The X-Files: I Want to Believe is a 2008 science fiction-thriller directed by Chris Carter and written by both Carter and Frank Spotnitz. It is the second feature film based on The X-Files franchise created by Carter, following the 1998 film. Three main actors from the television series, David Duchovny, Gillian Anderson and Mitch Pileggi, reappear in the film to reprise their respective roles as Fox Mulder, Dana Scully and Walter Skinner.

Unlike the first film, the plot does not focus on the series' ongoing extraterrestrial based mytharc themes, but instead works as a standalone thriller horror story, similar to many of the Monster-of-the-Week episodes that were frequently seen in the TV series. The story follows Mulder and Scully who have been out of the FBI for several years; with Mulder living in isolation as a fugitive from the organization and Scully having become a doctor at a Catholic-run hospital, where she has formed a friendly relationship with a seriously ill patient. But when an FBI agent is mysteriously kidnapped, and a former priest who has been convicted of being a child molester claims to be experiencing psychic visions of the endangered agent, Mulder and Scully reluctantly accept the FBI's request for their particular paranormal expertise on the case.

Gillian Leigh Anderson (born August 9, 1968) is an American actress. After beginning her career in theatre, Anderson achieved international recognition for her role as Special Agent Dana Scully on the American television series The X-Files. Her film work includes The House of Mirth (2000), The Mighty Celt (2005), The Last King of Scotland (2006), and two X-Files films, The X-Files (1998) and The X-Files: I Want to Believe (2008).

Anderson is of English and Irish descent, and was born in Chicago, Illinois, the daughter of Rosemary Anderson (née Lane), a computer analyst, and Edward Anderson, who owned a film post-production company. Soon after her birth, her family moved to Puerto Rico for 15 months; she then lived for five years in Roseberry Gardens, London N4, and finally for 15 months in Albany Road, London N4, so that her father could attend the London Film School. When Anderson was 11 years old, her family moved again, this time to Grand Rapids, Michigan. She attended Fountain Elementary and then City High-Middle School, a program for gifted students with a strong emphasis on the humanities; she graduated in 1986.